Place a tip of soldering iron to the solder joint and hold for a couple of seconds. Make sure that iron tip touches at the same time both the copper pad on circuit board and the component lead. Heating the only one part but not the other will result in poorly created joints. Thermal linkage is the area of contact between the iron tip and surface of solder joint. The contact between the iron tip and surface is usually very small straight line along iron tip. Thermal linkage can be significantly increased by adding a small amount of solder to the line of contact between iron tip and surface. Molten solder forms a heat bridge between the tip and the solder joint. This solder bridge provides the better and quicker transfer of heat into the solder joint.
Continue heating and then apply some solder to the solder joint, not to the tip of soldering iron. Solder should melt and flow smoothly onto the copper surface of pad filling a gap between component lead and copper pad. Two most common problems with soldering are adding too much or not enough solder.
All soldering operation should be completed in less than 2 seconds. The time of soldering operation depends on the temperature of your iron and size of the joint. If we keep applying heat longer than 2 seconds, this can break the pads or conductors on circuit board or damage temperature-sensitive components.
Remove the soldering iron while keeping the joint sill - do not move circuit board for a few seconds to allow the joint to cool down and solder to solidify.
Clean flux residues with ethanol alcohol or some other solvent.